The design of the trailing edge of an airfoil is preferably dictated by aerodynamic considerations. For improved aerodynamic performance, it is commonly preferred to provide a thin trailing edge for a gas turbine airfoil. However, thinness may result in weakness, and there are often structural limitations that limit the trailing edge design and necessitate the use of an aerodynamic design that is less than optimal.
It is known to use ceramic matrix composite (CMC) materials for airfoils and other components of gas turbine engines. CMC materials advantageously provide higher temperature capability than metal and a high strength to weight ratio. The reinforcing fibers of the CMC material are preferably wrapped around the trailing edge of an airfoil between the pressure and suction sides of the airfoil in order to provide strength to the trailing edge. However, the lower limit of the radius that may be made with a ceramic fiber may necessitate a trailing edge thickness that is greater than desired. Furthermore, the layer of ceramic insulating material that may be deposited over the CMC material in order to protect the CMC material from the hot working gas temperatures further exacerbates the trailing edge thickness issue.
U.S. Pat. No. 6,200,092 describes a gas turbine airfoil that includes a CMC leading edge segment and a separate monolithic ceramic chord segment that extends to a desirably thin trailing edge. However, because of the large aerodynamic loads imposed on the airfoil, it is necessary that the monolithic chord segment be formed of high strength structural ceramic, such as silicon nitride, and that it be supported separately from the leading edge segment with a special mounting arrangement. The separation between the segments also necessitates the use of a special seal there between, and it creates an undesirable gap along the airfoil surface. These design features and requirements adversely impact the cost, complexity and aerodynamic performance of the airfoil. Thus, further improvements in ceramic airfoil designs are desired.